The invention relates to an exhaust gas treatment device for an internal combustion engine of a motor vehicle.
Such an exhaust gas treatment device for an internal combustion engine of a motor vehicle is already known from US 2010/0005791 A1. The exhaust gas treatment device comprises at least one exhaust gas guide element having at least one exhaust gas conduit, through which exhaust gas of the internal combustion engine can flow. The exhaust gas guide element is thus used to guide the exhaust gas.
The exhaust gas treatment device further comprises a metering device, by means of which a reductant for denitrifying the exhaust gas can be introduced in the exhaust gas conduit at at least one feeding point. Furthermore, a flow separation element arranged in the exhaust conduit is provided, by means of which the exhaust gas conduit is divided into a first partial conduit and a second partial conduit.
A first partial flow of the exhaust gas can flow through the first partial conduit, wherein a second partial flow of the exhaust gas can flow through the second partial conduit. In other words, the exhaust gas or an overall flow of the exhaust gas is divided into the first partial flow and the second partial flow by means of the flow separation element, wherein the first partial flow flows through the corresponding first partial conduit and the second partial flow flows through the corresponding second partial conduit. The flow separation element comprises a conduit area, through which the second partial flow can flow and which expands in the flow direction of the second partial flow, and so at least in this portion, the flow separation element is designed as a cone.
Furthermore, DE 10 2009 053 950 A1 discloses a device for the treatment of exhaust gases in an exhaust gas system of internal combustion engines. Once again, a metering device for introducing reductants is provided.
Finally, WO 2012/047159 A1 discloses an exhaust gas treatment device having an exhaust gas guide element, through which exhaust gas can flow, and a metering device, with which a reductant can be introduced into the exhaust gas guide element.
The reductant is used to denitrify the exhaust gas. This means that the exhaust gas of the internal combustion engine, which for example is designed as a diesel engine, can contain nitric oxides (NOx) which, at least to some extent, are removed or eliminated by means of the reductant. For that purpose, the nitric oxides can, for example, react with ammonia (NH3) from the reductant to form nitrogen and water. For example, this reaction takes place in the course of a selective catalytic reduction (SCR), particularly in an SCR catalytic converter, through which the exhaust gas mixed with the reductant can flow, and which can be a component of the exhaust gas treatment device.
Usually, the reductant is an aqueous solution, particularly an aqueous urea solution which is introduced, particularly injected, into the exhaust gas conduit, e.g., by means of the metering device. It has become apparent that deposits and particularly urea deposits particularly in the interior of the exhaust gas treatment device or the exhaust gas guide element can occur.
The present invention therefore addresses the problem of further developing an exhaust gas treatment device of the initially described type such that excessive deposits of the reductant can be prevented.
In order to further develop an exhaust gas treatment device such that excessive deposits of the reductant, i.e., particularly excessive urea deposits, can be prevented, a second flow separation element, according to the invention, is provided in the second partial conduit. With the second flow separation element, the second partial conduit is divided or split into a first sub-conduit, a second sub-conduit, and a third sub-conduit. A first sub-flow of the exhaust gas can flow through the first sub-conduit, wherein the second sub-flow of the exhaust can flow through the second sub-conduit. In addition, the third sub-flow of the exhaust gas can flow through the third sub-conduit. The above sub-flows are each further partial flows of the second partial flow which thus comprises the sub-flows. In other words, the second partial flow which flows through the second partial conduit is divided into the sub-flows by means of the second flow element, and so the exhaust gas or an overall flow of the exhaust gas is divided not only by the first flow separation element into the first partial flow and the second partial flow, but is also further divided by the second flow separation element into the sub-flows.
For that purpose, the second flow separation element comprises a conduit area, through which the second sub-flow and the third sub-flow can flow, and which expands in the flow direction of the second sub-flow and the third sub-flow.
Preferably, the reductant can be introduced into the exhaust gas conduit by means of the metering device by forming a spray cone, the cone angle of which is at least 20 degrees, particularly preferably at least 25 degrees, wherein the flow separation elements are arranged entirely or safely outside of the spray cone. This means that the spray cone—when it is introduced or injected into the exhaust gas conduit—does not quite touch the flow separation elements. In other words, none of the flow separation elements is arranged within the real spray cone, and so the spray cone does not collide with the flow separation elements.
By means of the flow separation elements, the exhaust gas or its flow is divided multiple times until it reaches the metering device, particularly its nozzle, i.e., the feeding point. It is the task or the purpose of the partial flows and/or sub-flows, guided to the nozzle and preferably symmetrically to a spray axis, to support the metered reductant, i.e., its spray, and to reliably transport it out of the area near the nozzle, thus preventing deposits in the area. The remaining partial flows and/or sub-flows are supposed to provide for a widespread distribution of the spray on walls in the area away from the nozzle in order to keep the surface load and thus the cooling on the walls low. Since the spray is not applied to the components near the nozzle, particularly the flow separation elements, the deposit risk is kept low. As a result, the metering rates, at otherwise similar operating conditions, can be significantly increased, when compared to conventional exhaust gas treatment devices.
The subsequent advantages are that deposits in the area near and away from the nozzle can be kept low or prevented, and a low, at least substantially homogenous surface load of walls, to which the reductant was possibly applied, can be facilitated. As a result, the cooling can be kept at a minimum, and so the metered reductant can evaporate particularly well. In particular, particularly high metering quantities of the reductant can be realized. In addition, the exhaust gas back pressure can be kept low, resulting in particularly low fuel consumption.
In particular, it is preferably provided that the cone angle of the spray cone is greater than 20 degrees. It has proven to be particularly advantageous, when the cone angle is in a range from 25 degrees through 120 degrees. For example, respective contours of the flow separation elements, particularly on the side of the inner circumference, which are designed as components or installation elements, cling to the cone angle, also called spray cone angle, and so the installation space requirements can be kept particularly low.
The metering device, particularly its possibly provided nozzle for introducing the spray cone into the exhaust gas conduit, is usually designed on the basis of a nominal cone angle of the spray cone. In a first application, the nominal cone angle of the spray cone is, for example, 40 degrees, wherein the nominal cone angle in a second application is, for example, 60 degrees. With a tolerance of the measuring methods for recording the cone angle, and a component tolerance of the metering device, particularly the nozzle, this results in an actual cone angle of the spray cone of 30 to 50 degrees in the first application, and an actual cone angle of 50 to 70 degrees in the second application. In other words, there is usually a tolerance of the cone angle of +/−10 degrees. In the second application with the nominal cone angle of 60 degrees, the cone angle is determined, for example, in addition to the tolerance of +10 degrees for the actual cone angle, by an additional+20 degrees, thus resulting in overall 90 degrees, and so the aforementioned components cling to this cone angle of 90 degrees. As a result, the components are with additional certainty not struck by the spray cone or spray drops of the spray cone. By taking into account the aforementioned tolerances, a sufficient distance of the components from the spray cone can thus be realized. In particular, this means that the components are definitely not struck by the spray cone.
Since the first conduit area expands, the first flow separation element or the first conduit area is designed as a cone. The second flow separation element or the second conduit area is also designed as a cone. By using not only the first flow separation element but also the second flow separation element, the overall flow of the exhaust gas can be divided multiple times, before the exhaust gas reaches the feeding point and thus reaches, for example, a nozzle, which is arranged at the feeding point, and with which the reductant is introduced into the exhaust gas guide element. The purpose of the sub-flows guided to the nozzle is particularly that of supporting the reductant. The spray cone is also called jet cone or simply jet or spray, and so the reductant is introduced into the exhaust gas guide element, while forming an at least substantially conical jet or spray which forms the spray cone. The sub-flows thus have the purpose of supporting the spray and reliably transporting it out of an area near the nozzle in order to prevent deposits of the reductant in the area. The remaining sub-flows and the first partial flow provide for a widespread distribution of the spray or the reductant at wall areas in areas away from the nozzle, in order to at least keep the so-called surface load and thus the cooling of the exhaust gas guide element at least low. As a result, the risk of deposits of the reductant can be kept particularly low.
At otherwise similar operating conditions, it is thus possible with the exhaust gas treatment device according to the invention to realize particularly high metering rates, when compared to conventional exhaust gas treatment devices, i.e., to introduce particularly great quantities of the reductant into the exhaust gas guide element without creating excessive deposits. Despite particularly high metering rates and low temperatures, a particularly advantageous urea concentration without or only very little deposit formation can be realized with the use of the second flow separation element. It is particularly possible to prevent deposits both in the areas near and away from the nozzle. Since the surface load of wall areas, to which the reductant is also applied, can be kept low, the cooling of the wall areas can also be kept low. This results in a particularly advantageous evaporation of the introduced quantity of reductant.
Due to the advantageous concentration of the reductant, which can be effected by means of the second flow separation element, the reductant being, for example, an aqueous urea solution, great quantities of the reductant can also be introduced in order to be able to denitrify the exhaust gas particularly well. It is particularly possible to realize a particularly advantageous mixing of the ammonia released by the reductant before it enters an SCR catalytic converter; as a result, particularly high conversions can be generated in the SCR catalytic converter (SCR—selective catalytic reduction). It is further advantageous that, despite the use of the second flow separation element and particularly its specific design, the exhaust gas back pressure can be kept low, and so the exhaust gas treatment device according to the invention allows for a particularly efficient operation, i.e., with low fuel consumption of the internal combustion engine. Therefore, the use of the second flow separation element has an at least almost neutral effect with regard to fuel consumption.
In an advantageous embodiment of the invention, at least one part of the exhaust gas conduit, through which the exhaust gas can flow, is volute-shaped. This means that at least one part of the exhaust gas conduit, particularly at least one of the partial conduits and/or at least one of the sub-conduits, has the shape of a spiral or a volute, and so at least this part tapers along its direction or along a direction, in which the exhaust gas flows through the volute-shaped part. Based on a state, in which the spray cone is introduced, particularly injected, into the exhaust gas conduit, at least this part of the exhaust gas conduit thus extends in a volute- or spiral-shaped manner in circumferential direction of the spray cone over its circumference.
It is further conceivable that at least one of the flow separation elements, particularly, the first flow separation element, has on its inner side a contour of a diffuser.
In a further advantageous embodiment, the second conduit area is at least to some extent arranged in the first conduit area. In other words, it is, for example, provided that the second conduit area protrudes at least to some extent into the first conduit area. As a result, a particularly advantageous flow separation and flow guidance of the exhaust gas can be realized, and so the risk of deposits can be kept particularly low.
It has proven particularly advantageous, when the reductant can be introduced, particularly injected, into the second conduit at an injection direction, wherein the conduit areas each expand along the injection direction. In other words, the injection direction coincides with a direction, in which the conduit areas expand. This means that each of the conduit areas has a passage direction, in which the exhaust gas can flow through the conduit areas. The corresponding passage direction coincides with the injection direction. Since the jet or the spray of the reductant, for example, reaches the conduit areas at least to some extent, the risk of deposits can be kept particularly low.
A further embodiment is characterized in that the reductant, while forming the spray cone (jet or spray), can be introduced into the second partial conduit along an imaginary straight line, which coincides with the injection direction, wherein the conduit areas each are arranged coaxially to the straight line. In other words, it is preferably provided that the straight line coincides with corresponding central axes of the conduit areas. As a result, an excessive deposit of reductants on wall areas can be prevented.
Since the jet or spray is at least substantially conical or frusto-conical, it is preferred that the imaginary straight line coincides with the central axis of the cone or frustum, i.e., with the central axis of the jet cone.
In a particularly advantageous embodiment of the invention, the first partial conduit is delimited by a first surface area of the first flow separation element, and a first part of an inner side of the exhaust gas guide element which faces the first surface area, wherein the second partial conduit is delimited by a second surface area of the first flow separation element which faces away from the first surface area, and a second part of the inner side of the exhaust gas guide element which faces the second surface area. As a result, a particularly advantageous flow separation can be realized, and so excessive deposits of the reductant can be reliably prevented. It is further possible to realize a particularly advantageous flow guidance, and so the exhaust gas back pressure in the exhaust gas treatment device can be kept low.
In order to realize a particularly advantageous flow guidance and flow separation, it is provided in a further embodiment of the invention that the first sub-conduit is delimited by a third part of the second surface area of the first flow separation element, and a third surface area of the second flow separation element which faces the third part, wherein the third sub-conduit is delimited by a fourth surface area of the second flow separation element which faces away from the third surface area, and a fifth surface area of the second flow separation element which faces the fourth surface area.
Furthermore, it has proven particularly advantageous if the second sub-conduit is delimited by a sixth surface area of the second flow separation element which faces away from the fifth surface area, and a partial area, facing the sixth surface area, of the second part of the inner side of the exhaust gas guide element. As a result, a particularly advantageous flow guidance and flow separation can be realized, and so excessive deposits can be prevented.
A further embodiment is characterized in that straight guide elements for guiding the exhaust gas are associated with the third sub-conduit. The straight guide elements are, for example, straight blades which are essentially designed so as to be plane or flat or planar, thus allowing for an at least substantially symmetrical inflow at the nozzle.
For realizing a particularly symmetrical inflow at the nozzle, it is, for example, possible to use a substantially vertical guide element, particularly in the form of a metal sheet.
In a further advantageous embodiment of the invention, curved guide elements are provided for effecting an at least substantially swirl-shaped flow of at least one part of the exhaust gas. By means of the curved guide elements which, for example, are designed as curved blades, a swirl-shaped flow can be applied to at least one part of the exhaust gas, and so an advantageous turbulence of the exhaust gas is presentable. Due to this turbulence, the exhaust gas can be mixed particularly well with the reductant, and so a particularly good processing of the reductant is generated. As a result, excessive deposits can be prevented.
It has been proven particularly advantageous if the curved guide elements are arranged in the second partial conduit. As a result, a swirled flow can be realized in the second conduit area, i.e., in the inner, second cone. The objective is that of preventing a detachment or a flow detachment in the inner cone despite the large opening angle of the inner cone.
In a further embodiment of the invention, at least one of the flow separation elements, particularly the first flow separation element, has on its inner side a contour of a diffusor with a first longitudinal area, which is tapered in flow direction of the corresponding partial flow or sub-flow, and an expanding second longitudinal area adjacent to the first longitudinal area in flow direction.
Further advantages, features, and details of the invention can be derived from the following description of a preferred embodiment and by means of the drawings. The features and combinations of features specified in the above description as well as the following features and combinations of features specified in the drawing descriptions and/or only shown in the drawings can not only be used in the specific combination described but also in different combinations or on their own without exceeding the scope of the invention.